1. Field of the Invention
This invention relates to a center pivot irrigation system and more particularly to an alignment control for long center pivot systems.
2. Description of the Related Art
Conventional center pivot irrigation systems comprise an elongated water pipe pivotally connected at its inner end to a center pivot structure and extending outwardly therefrom. The water pipe of the conventional center pivot system is comprised of a plurality of pipes connected together in an end-to-end fashion which are supported upon a plurality of drive units. Each of the drive units may be propelled by an electric motor, a hydraulic motor or an air motor, with electric motors being the most popular and widely used source of propulsion. Normally, the outermost drive unit or last drive unit is the master unit with the other drive units being selectively driven in response to angular displacement of the pipe section adjacent thereto.
The machine alignment on the center pivot system is maintained by a mechanical linkage at each drive unit span joint, which operates a micro-switch, which in turn starts and stops the electric motor on the drive unit to keep it alignment with the next span. The alignment control works well on most machines, up to approximately 1,500 feet in length, but does not always maintain good alignment on longer systems. The reason for the problem on long systems is that small changes in alignment at a number of drive units on the system can cause a large change in the overall system alignment. If the alignment gets bad enough, it can cause structural damage to the system. These small changes in alignment are causes by external forces such as the drive unit crossing crop furrows at an angle, strong wind blowing on the spans, or temperature changes in the micro-switches and linkages.